Lymph node metastasis is the spread (metastasis) of cancer cells into a lymph node. Lymph node metastasis is different from malignant lymphoma. Lymphoma is a cancer of lymph node, rather than cancer in the lymph node, because lymphoma originates from the lymph node itself, instead of originating elsewhere (e.g., the breast or colon) and spreading to the lymph nodes. Pathology Generally, metastases form first in the lymph nodes that are closest to the primary tumor. This is because the lymphatic fluid (lymph) of the cancerous organ or tissue flows first to these nearby lymph nodes. The tumor cells reach the lymph nodes via this lymphatic pathway, where they remain and proliferate. These spreading cancer cells grow in the lymph nodes, which causes the affected lymph nodes to get bigger. Lymphogenic metastasis is a type of regional metastases. This is in contrast to distant metastases, such as bone metastases, liver metastases or brain metastases, which could come from any part of the body. Tumor cells that grown in the lymph nodes can later detach from the lymph node metastases, enter the bloodstream, and lead to distant metastases via hematogenous spread. However, the science is not settled on this point, and there is disagreement about whether metastases can metastasize themselves. The probability of metastasis in the lymph nodes depends on the density of the lymphatic vessels in the area of the primary tumor. For example, hypopharyngeal or nasopharyngeal carcinomas metastasize extremely quickly to the nearby tissue areas, which are rich in lymphatic vessels. Classification Lymph node metastases are usually classified according to the TNM staging system (T = tumor, N = nodes = lymph nodes, M = metastasis). N0 means that there are no signs of lymph node involvement, and the numbers indicate increasing levels of spread to lymph nodes. However, staging systems varies according the type of primary tumor. Frequency The probability of metastasis to lymph nodes depends on the nature of the primary tumor. In the case of sarcomas, for example, lymph nodes are only very rarely affected. In the case of the much more common carcinomas, especially for the particularly aggressive types, the probability is considerably higher. Above all, however, it depends on the local spread of the primary tumor, its infiltration level, and the tumor size. In many carcinomas, the first metastases are found in the lymph nodes. These include, for example, pancreatic cancer, head and neck cancer